WO2008059901A1

WO2008059901A1 - PROCESS FOR PRODUCTION OF GaN CRYSTALS, GaN CRYSTALS, GaN CRYSTAL SUBSTRATE, SEMICONDUCTOR DEVICES, AND APPARATUS FOR PRODUCTION OF GaN CRYSTALS

Info

Publication number: WO2008059901A1
Application number: PCT/JP2007/072135
Authority: WO
Inventors: Yusuke Mori; Takatomo Sasaki; Fumio Kawamura; Masashi Yoshimura; Minoru Kawahara; Yasuo Kitaoka; Masanori Morishita
Original assignee: Osaka University; Osaka Industrial Promotion Organization
Priority date: 2006-11-14
Filing date: 2007-11-14
Publication date: 2008-05-22
Also published as: KR20090082475A; CN101583745A; JPWO2008059901A1; EP2103721A4; EP2103721A1; CN101583745B; US8187507B2; ATE541074T1; KR101192061B1; JP2010189270A; JP5305359B2; US20100059717A1; EP2103721B1; JP4538596B2

Abstract

The invention provides a process for the production of GaN crystals which can realize at least either of the prevention of nucleation and the growth of high-quality nonpolar planes. The invention relates to a process of producing GaN crystals in a melt containing both an alkali metal and gallium as the essential components which comprises the step of adjusting the carbon content of the melt and the step of reacting the gallium with nitrogen. The process can realize the prevention of nucleation and/or the growth of nonpolar planes as shown in Fig. 4.

Description

Specification

GaN crystal manufacturing method, GaN crystal, GaN crystal substrate, semiconductor device, and GaN crystal manufacturing device

Technical field

The present invention relates to a GaN crystal manufacturing method, a GaN crystal, a GaN crystal substrate, a semiconductor device, and a GaN crystal manufacturing apparatus.

Background art

[0002] Group III element nitride crystal semiconductors are used in the fields of, for example, heterojunction high-speed electronic devices and photoelectric devices (semiconductor lasers, light-emitting diodes (LEDs), sensors, etc.). (GaN) crystals are attracting attention. Conventionally, in order to obtain a single crystal of gallium nitride, gallium and nitrogen gas are directly reacted (see Non-Patent Document 1). In this case, 1300 ~; 1600. C, from 8000 to 17000 atm (about 800 to 1700 MPa) is required. In order to solve this problem, a technique for growing a gallium nitride single crystal in a sodium (Na) flux (melt) (hereinafter also referred to as “Na flux method”) has been developed (for example, patent literature). ;!-3, see Non-Patent Documents 2 and 3). According to this method, the heating temperature is greatly reduced to 600 to 800 ° C, and the pressure can be reduced to about 50 atm (about 5 MPa). In the Na flux method, there is a method in which a seed crystal is put in the Na flux in advance and the crystal is grown using this seed crystal as a nucleus. According to this method, a Balta size crystal can be obtained. As the seed crystal, when a GaN single crystal is grown, for example, a laminated substrate in which a GaN crystal thin film layer is formed on a sapphire substrate by MOCVD method or HVPE method is used. Such technology is also called “liquid phase epitaxial growth method”!

[0003] Among electronic devices using GaN single crystals, application to illumination of light emitting diodes (LEDs) is expected, and research and development are thriving. This is because an LED using a GaN single crystal can save a great deal of power compared to conventional lighting fixtures such as fluorescent lamps. However, LEDs using conventional GaN single crystals have limitations in improving brightness, and could not achieve the theoretically predicted level of high brightness. There are three reasons for this: Because there is a problem.

(1) Charge bias inside the LED

(2) Change in emission wavelength due to higher brightness

(3) Presence of a high resistance part inside the LED

[0004] The above three problems (1) to (3) can be theoretically solved by fabricating an LED on a nonpolar surface of a GaN crystal substrate. The nonpolar surface is a surface having no charge bias. However, with conventional technology, it was impossible to fabricate LEDs on the nonpolar surface of a GaN crystal substrate. Figure 1 shows the basic LED configuration. As shown in the figure, the LED is formed on a substrate 1 made of sapphire or silicon carbide, on a low-temperature buffer layer 2, a GaN crystal (Si-doped) layer 3, an n-AlGaN (Si-doped) layer 5, and an InGaN layer 6 P-AlGaN (Mg-doped) layer 7, p-GaN (Mg-doped) layer 8, transparent electrode layer 9 and p-layer electrode 10 are laminated in this order, and the GaN crystal (Si-doped) layer 3 The n-layer electrode 4 is arranged on a part of the!! In conventional LED fabrication, as shown in FIG. 2, a GaN crystal layer 3 is grown on a substrate 1 such as sapphire via a low-temperature buffer layer 2 by a liquid phase epitaxial growth method. The GaN crystal can grow only on the c-plane, and the side surface 32 of the GaN crystal layer 3 becomes the M-plane, but the upper surface 31 of the GaN crystal layer 3 becomes the c-plane. In addition, even if an attempt is made to forcibly form a non-polar surface such as an M-plane, the actual situation is that the brightness cannot be improved due to the poor quality of the crystals obtained.

[0005] Furthermore, in the liquid phase epitaxial growth method using Na flux (melt), nuclei other than seed crystals are generated in the flux, which causes the quality and yield of GaN crystals to deteriorate. There is. The graph in Fig. 8 shows an example of the relationship between the nitrogen gas pressure and the thickness (film thickness) of the GaN crystal formed on the substrate. As shown in the figure, when the pressure of nitrogen gas is increased, the force S that increases the thickness of the GaN crystal S, and when the nitrogen gas pressure exceeds a certain point (about 34 atm in Fig. 8), the thickness of the GaN crystal is reversed. Go thin. This is because, as shown in the figure, nuclei other than seed crystals are generated in the Na flux.

[0006] As described above, the problem of nonpolar plane growth and the problem of nucleation are important problems to be solved in the production of GaN crystals. However, there are other methods for producing Group III element nitride crystals. However, it is an important problem to be solved. Patent Document 1: Japanese Patent Application Laid-Open No. 2000-327495

Patent Document 2: Japanese Patent Laid-Open No. 2001-102316

Patent Document 3: Japanese Patent Laid-Open No. 2003-292400

Non-Patent Document 1: J. Phys. Chem. Solids, 1995, 56, 639

Non-Patent Document 2: Journal of Japanese Society for Crystal Growth 30, 2, pp38 -45 (2003)

Non-Patent Document 3: J. J. Appl. Phys. 42, ppL879-L881 (2003)

Disclosure of the invention

[0008] Therefore, the present invention provides a GaN crystal manufacturing method, a GaN crystal, a GaN crystal substrate, a semiconductor device, and a GaN crystal manufacturing capable of realizing at least one of prevention of nucleation and growth of a highly crystalline nonpolar surface. An object is to provide an apparatus.

[0009] In order to achieve the above object, the production method of the present invention is a method of producing a GaN crystal in a melt containing at least an alkali metal and gallium (Ga),

An adjusting step of adjusting the carbon content in the melt;

A reaction step in which the gallium (Ga) and nitrogen react;

A GaN crystal manufacturing method.

[0010] The GaN crystal of the present invention has a non-polar surface as a main surface, the full width at half maximum of the rocking curve by two-crystal method X-ray diffraction is in the range of more than 0 to 200 seconds, and the dislocation density is 0. Over 1

0 GaN crystals in a range of ⁶ pieces / cm ² or less.

[0011] The GaN crystal substrate of the present invention includes the GaN crystal of the present invention, and the nonpolar surface is a substrate surface on which a semiconductor layer is formed.

[0012] A semiconductor device of the present invention includes the GaN crystal substrate of the present invention, and is formed on the substrate surface.

A semiconductor device in which a semiconductor layer is formed.

[0013] The GaN crystal production apparatus of the present invention is a production apparatus for producing a GaN crystal in a melt containing at least an alkali metal and gallium,

A preparation unit for adjusting the content of carbon in the melt;

The GaN crystal manufacturing apparatus includes a reaction section where the gallium and nitrogen react.

[0014] As a result of a series of studies to achieve the above object, the present inventors have adjusted the carbon content in the melt containing an alkali metal (for example, containing carbon in the melt). Let The inventors have found that at least one of prevention of nucleation in the melt and growth of a high-quality nonpolar surface can be realized, and the present invention has been made. Further, as described above, the GaN crystal of the present invention has a nonpolar surface as a main surface, and has physical properties of a full width at half maximum of the rocking curve within a predetermined range and a dislocation density within the predetermined range. Has higher crystallinity than those produced by conventional methods such as the gas phase method. Such a high-quality GaN crystal of the present invention can be produced by the production method of the present invention, but the force production method is not limited to this. The “main surface” refers to the widest surface in the crystal.

Brief Description of Drawings

FIG. 1 is a configuration diagram illustrating an example of a semiconductor device.

FIG. 2 is a configuration diagram showing an example of a GaN crystal formed on a substrate.

FIG. 3 is a structural diagram showing an example of a GaN crystal formed on the substrate of the present invention.

FIG. 4 is a photograph of a GaN crystal in Example 1 of the present invention.

FIG. 5 is another photograph of the GaN crystal in Example 1.

FIG. 6 is a photograph of a GaN crystal in Comparative Example 1.

FIG. 7 is a graph showing the relationship between the carbon addition ratio and the crystal yield in Example 1 and Comparative Example 1.

FIG. 8 is a graph showing an example of the relationship between nitrogen gas pressure and GaN crystal thickness (film thickness).

FIG. 9 is a graph showing the relationship between the carbon addition ratio and the crystal yield in Example 2 and Comparative Examples 2 to 3 of the present invention.

FIG. 10 is a graph showing the relationship between the carbon addition ratio and crystal yield in Example 3 and Comparative Examples 4 to 6 of the present invention.

FIG. 11 is a configuration diagram showing an example of a manufacturing apparatus used in the method for manufacturing a GaN crystal of the present invention.

FIG. 12 is a photograph of a GaN single crystal in Example 4 of the present invention.

FIG. 13 is a schematic diagram showing an example of the structure of a GaN crystal.

BEST MODE FOR CARRYING OUT THE INVENTION In the production method of the present invention, the adjusting step includes at least one of a removing step of removing a part of carbon in the melt and an adding step of adding carbon to the melt. Is preferred.

[0017] The production method of the present invention includes a seed crystal providing step of providing a seed crystal in the melt, and the seed crystal is preferably a GaN crystal.

[0018] In the production method of the present invention, the form of the carbon is not particularly limited, and may be a single element of carbon or a carbon compound!

In the production method of the present invention, the seed crystal is preferably a GaN crystal layer formed on a substrate.

[0020] In the production method of the present invention, by adjusting the carbon content in the melt (for example, by containing carbon in the melt), in the melt other than the seed crystal. It is preferable to prevent the generation of crystal nuclei. In this case, the content ratio of carbon in the melt is, for example, in the range of 0.;! To 5 atom% with respect to the total of the melt, the gallium, and the carbon.

[0021] In the production method of the present invention, by adjusting the carbon content in the melt (for example, by containing carbon in the melt), the nonpolar plane of the GaN crystal is grown. It is preferable to make it. In this case, the content ratio of carbon in the melt is, for example, in the range of 0.3 to 8 atomic% with respect to the total of the melt, the gallium, and the carbon. In the production method of the present invention, a surface other than the nonpolar surface may be grown, and this surface may be cut to expose the nonpolar surface on the surface.

In the production method of the present invention, the seed crystal is preferably a GaN crystal layer on a substrate. In this case, it is preferable to grow at least one of the M-plane and the a-plane by adjusting the carbon content in the melt (for example, by containing carbon in the melt). Furthermore, in this case, it is preferable that the upper surface of the GaN crystal layer of the substrate is a nonpolar plane (at least one of the a plane and the M plane). However, the manufacturing method of the present invention is not limited to this, and a plane other than the M-plane and the a-plane and other than the c-plane may be grown. That is, in the manufacturing method of the present invention, when a GaN crystal is grown, an angular force S formed on the M plane and the a plane is grown, and a plane smaller than the c plane is grown, and the grown plane is cut. Then, the M face or a face may be exposed on the surface.

[0023] In the production method of the present invention, the melt is preferably a melt containing Na, for example.

[0024] The production method of the present invention may further include a stirring step of stirring the melt. The step of performing the stirring step is not particularly limited, and may be performed, for example, at least one before the reaction step, simultaneously with the reaction step, and after the reaction step. More specifically, for example, it may be performed before the reaction step, simultaneously with the reaction step, or both.

[0025] The GaN crystal of the present invention may contain carbon. The GaN crystal of the present invention is preferably produced by the production method of the present invention.

[0026] The semiconductor device of the present invention is preferably, for example, an LED, a semiconductor laser, or a power high-frequency electronic element.

[0027] Next, the present invention will be described in detail.

[0028] As described above, the production method of the present invention is a method for producing a GaN crystal in a melt containing at least an alkali metal and gallium, and is an adjustment for adjusting the carbon content in the melt. And a reaction step in which gallium and nitrogen react. The adjustment step may include at least one of a removal step of removing a part of carbon in the melt and an addition step of adding carbon to the melt.

Furthermore, a seed crystal providing step for providing a seed crystal containing a group III element nitride may be included in the melt.

For example, the manufacturing method of the present invention is a GaN crystal manufacturing method in which a GaN crystal is grown by reacting gallium and nitrogen with a GaN seed crystal that has been put in advance in a melt containing an alkali metal. In the manufacturing method, carbon is contained in the melt to grow the GaN crystal. The present invention is also a method for controlling a growth surface of a GaN crystal by containing carbon in the melt in the method for producing the GaN crystal, and / or generating nuclei in the melt. It is also a way to prevent this.

[0029] The alkali metal in the melt functions as a flat in the liquid phase epitaxial growth method. The alkali metal is lithium (Li), sodium (Na), potassium (K ), Norevidium (Rb), cesium (Cs) and francium (Fr), of which Li and Na are preferred, and Na is more preferred. The melt may contain other components, for example, gallium (Ga) and nitrogen (N), which are raw materials for GaN crystals, and flux raw materials other than alkali metals. The nitrogen is not limited in its form such as gas, nitrogen molecule, nitrogen compound and the like. Examples of the flux raw material include alkaline earth metals, and specific examples include calcium (Ca), magnesium (Mg), strontium (Sr), norlium (Br), and radium (Ra). Among them, Ca is more preferable than Ca and Mg. The addition ratio of the alkali metal to gallium is, for example, 0.;! To 99.9 mol%, preferably;! To 99 mol%, more preferably 5 to 98 mol%. In addition, the molar ratio when using a mixed flux of alkali metal and alkaline earth metal is, for example, anolelic metal: anolelic earth metal = 99. 99—0. 01: 0. 01—99. 99, Preferably (between 99.9 and 0.05: 0.1-99.95, more preferably 99.5-1: 0.5-99. The purity of the melt is preferably high. The purity of Na is preferably 99.95% or more, and high-purity flux components (for example, Na) may be commercially available products of high purity, or may be distilled after purchase of commercial products. You may use what raised purity by methods, such as.

[0030] The reaction conditions between gallium and nitrogen are, for example, a temperature of 100 to; 1500 ° C, a pressure of 100 Pa to

20 MPa, preferably 300 to 1200; C, pressure 0. OlMPa ~;! OMPa, more preferably 500 ~; 1100 ° C, pressure 0.1MPa ~ 6MPa. The reaction is preferably carried out in a nitrogen-containing gas atmosphere. This is because the nitrogen-containing gas dissolves in the flats and becomes a raw material for growing GaN crystals. The nitrogen-containing gas is, for example, nitrogen) gas, ammonia (NH 2) gas, etc., and these may be mixed at a mixing ratio

twenty three

Is not limited. In particular, the use of ammonia gas is preferable because the reaction pressure can be reduced.

[0031] In the production method of the present invention, the seed crystal may be dissolved by the flux until the nitrogen concentration increases. In order to prevent this, it is preferable that nitride is present in the flux at least at the initial stage of the reaction. Examples of the nitride include CaN, LiN, NaN, BN, SiN, InN, and the like.

3 2 3 3 3 4

It may be used alone or in combination of two or more. In addition, the nitride of the nitride The ratio in tas is, for example, 0.0001 mol% to 99 mol%, preferably 0.00 lmol% to 50 mol%, more preferably 0.005 mol% to 10 mol%.

[0032] In the production method of the present invention, impurities may be present in the mixed flux. In this way, an impurity-containing GaN crystal can be produced. Examples of the impurities include silicon (Si), alumina (Al 2 O 3), indium (In), aluminum (A1), and nitrogen.

twenty three

Indium phosphide (InN), silicon oxide (SiO 2), indium oxide (In 2 O 3), zinc (Zn), magne

2 2 3

Examples include shim (Mg), zinc oxide (ZnO), magnesium oxide (MgO), and germanium (Ge).

[0033] As described above, the carbon content in the melt is adjusted. For example, in order to make the carbon content a predetermined amount, at least one of a step of removing a part of carbon in the melt and a step of adding carbon to the melt is performed. The carbon may be a simple carbon or a carbon compound. Preferred are simple carbon and carbon compounds that generate cyan (CN) in the melt. Carbon may be a gaseous organic substance. Examples of such carbon simple substance and carbon compound include cyanide, graphite, diamond, fullerene, carbon nanotube, methane, ethane, propane, butane, and benzene. The carbon content is not particularly limited. For the purpose of preventing nucleation in the melt, when performing at least one of the step of adding carbon to the melt and the step of removing a part of carbon in the melt, the melt, Based on the sum of the gallium and the carbon, for example, 0.0;! To 20 atoms (at.)% Range, 0.05 to 15 atoms (at.)% Range, 0.;! To 10 Atom (at.)% Range, 0;;! To 5 atom (at.)% Range, 0.25-7. 5 atom (at.)% Range, 0.25 to 5 atom (at.) % Range, 0.5 · 5 to 5 atom (at.)% Range, 0.5 to 2.5 · 5 atom (at.)% Range, 0.5 to 2 atomic (at.)% Range, 0 In the range of 5 to 1 atom (at.)%, In the range of 1 to 5 atom (at.)%, Or in the range of! To 2 atom (at.)%. Among these, the range of 0.5 · 5 to 5 atoms (at.)%, The range of 0.5 to 2.5 atoms (at.)%, The range of 0.5 · 2 to 2 atoms (at.)%, A range of ~ !! atom (at.)%, A range of 1-5 atom (at.)%, Or a range of 1-2 atom (at.)% Is preferred. When performing at least one of the step of adding carbon to the melt and the step of removing a part of the carbon in the melt for the purpose of growing a non-polar surface of the GaN crystal, the melt, Based on the sum of the gallium and the carbon, for example, 0.0;! To 25 atoms (at.)% Range, 0.05 to 20 atoms (at.)% Range, 0.5 to 15 atoms (At.)% Range, 0.3-8 atoms (at.)% Range, 0.75-; 10 atoms (at.)% Range, 1 · 0-5 atoms (at.)% Range Or within the range of 2 · 0-5 atoms (at.)%. Among these, a range of 1 · 0 to 5 atoms (at.)% Or a range of 2.0 to 5 atoms (at.)% Is preferable. The “melt” in the total of the melt, the gallium and the carbon means the total of the components constituting the melt. For example, when the melt is a flux of Na alone, it means only Na, and when it is a mixed flux of Na and Ca, it means the sum of Na and Ca.

As described above, the seed crystal is preferably a GaN layer formed on a substrate. As the substrate, the sapphire substrate, the silicon carbide (SiC) substrate, or the like can be used. The GaN layer may be, for example, a crystal or may be amorphous, and in the case of a crystal, it may be a single crystal or a polycrystal. Good. The form of the GaN layer is not particularly limited, but for example, the form of a thin film layer is preferable. The thickness of the thin film layer is not particularly limited. For example, 0.005 to 100000 111, 0.00;! To 50000 m, 0.01 to 5000 ^ 111, 0.01 to 500 ^ 111, 0 01 ~ 50 ^ 111, 0. 1 ~ 50 ^ 111, 0. 1 ~ 10 ^ m, 0.;! ~ 5〃m, !! ~ 10〃m or;! ~ 5〃m. The surface (upper surface) of the GaN crystal layer is preferably a nonpolar plane of either the M plane or the a plane. If the surface (upper surface) of the GaN crystal layer on the substrate is a nonpolar surface, as shown in FIG. 2, by adding carbon to the melt, the GaN crystal layer 2 on the substrate 1 A GaN crystal 3 having a smooth nonpolar surface 31 on the surface can be grown. In this case, the side surface 32 of the GaN crystal 3 is a c-plane. On the other hand, when the surface (upper surface) of the GaN crystal layer on the substrate is the c-plane, when carbon is added to the melt, it is formed on the GaN crystal layer 2 as shown in FIG. The upper surface (surface) 31 of the GaN crystal 3 has a polygonal cross section. This is also the force by which both the a-plane and the M-plane grow in the GaN crystal 3 grown on the surface force _Sc plane of the GaN crystal layer 2. In FIG. 3, the side surface 32 of the GaN crystal 3 is a c-plane. Even a GaN crystal having such a cross-section with a polygonal surface (upper surface) can be put to practical use if the surface is polished to a smooth surface. The thin film layer may be formed, for example, by metal organic chemical vapor deposition (MOCVD) or halide vapor deposition. It can be formed on the substrate by the long method (HVPE), the molecular beam epitaxy method (MBE method) or the like. The maximum diameter of the thin film layer is, for example, 2 cm or more, preferably 3 cm or more, more preferably 5 cm or more, and the upper limit is not limited as it is larger. In addition, since the standard of the bulk compound semiconductor is 2 inches, from this viewpoint, the size of the maximum diameter is preferably 5 cm. In this case, the range of the maximum diameter is, for example, 2 to 5 cm. It is preferably 3 to 5 cm, more preferably 5 cm. The maximum diameter is, for example, the length of the longest line that connects a point on the outer periphery of the surface of the thin film layer with another point.

In the production method of the present invention, it is not always necessary to put a seed crystal of GaN as a crystal nucleus in advance in a melt containing an alkali metal. As long as the carbon content in the melt is adjusted to a predetermined amount, the above-described effects of the present invention (prevention of nucleation in the melt can be avoided) even if a GaN seed crystal is not added as a crystal nucleus in advance. And at least one of the growth of high quality non-polar surfaces is feasible).

In the case of providing a seed crystal containing GaN in the melt, the GaN crystal can be easily grown as compared to the case of not providing the seed crystal.

Here, the structure of the GaN crystal will be described based on the schematic diagram of FIG. As shown, in the GaN crystal, the M plane and the a plane are parallel to the c axis, in other words, the M plane and the a plane are orthogonal to the c plane. And the a-plane exists in the direction of the middle angle between the two adjacent M-planes. These relationships hold even if the M and a planes are reversed.

[0036] In the method for producing a GaN crystal of the present invention, the GaN crystal to be produced may be, for example, either a single crystal or a polycrystal, but is preferably a single crystal.

[0037] Next, as described above, the GaN crystal production apparatus of the present invention is a production apparatus for producing a GaN crystal in a melt containing at least an alkali metal and gallium. An apparatus for producing a GaN crystal, comprising a preparation unit for adjusting the carbon content and a reaction unit for reacting the gallium and nitrogen. The manufacturing method of the present invention may be performed using any manufacturing apparatus, but is preferably performed using, for example, the GaN crystal manufacturing apparatus of the present invention. FIG. 11 shows an example of the GaN crystal production apparatus of the present invention. The GaN crystal production apparatus of the present invention includes an adjustment unit that adjusts the carbon content in the melt, and a reaction unit in which gallium and nitrogen react. With. As shown in the figure, this apparatus includes a gas tank 11, a pressure regulator 12, an electric furnace 14, a heat and pressure-resistant container 13, and a vacuum pump 17. An example of the electric furnace 14 is a resistance heater. The electric furnace 14 may use a heat insulating material. When the resistance heater is used at a temperature of 1000 ° C. or lower, a cantilever wire can be used as a heating element, thereby simplifying the configuration of the apparatus. In addition, when heating up to 1500 ° C. in the resistance heating heater, MoSi or the like is used. Gas tank 1

2

1 is filled with a nitrogen-containing gas such as nitrogen gas or ammonia gas. The gas tank 11 and the vacuum pump 17 are connected to the pressure and heat resistant container 13 by pipes, and the pressure regulator 12 is disposed in the middle thereof. The pressure regulator 12 can adjust the gas pressure to, for example, a gas pressure of! ~ LOOatm and supply the nitrogen-containing gas into the pressure-resistant heat-resistant container 13, and the pressure can be reduced by the vacuum pump 17. In the figure, 16 is a leak valve. As the pressure and heat resistant container 13, for example, a stainless steel container or the like is used. The heat-resistant and pressure-resistant container 13 is disposed in the electric furnace 14 and is heated by heat. A crucible 15 is arranged in the heat-resistant pressure-resistant container 13, and materials such as alumina (Al 2 O 3), tungsten (W), platinum (Pt), and SUS are used as the crucible material.

twenty three

Is used. A crucible formed from a carbon-based material such as a graphite crucible or a silicon carbide crucible may be used. However, even if a crucible formed from a carbon-based material is used, the amount of carbon eluted from the crucible is so small that the effect of the present invention cannot be obtained unless carbon is added separately. In the crucible 15, gallium (Ga) as a crystal raw material, alkali metal (Na or the like) and carbon (for example, graphite) as a melt raw material are put. In the present invention, other components may be put in the crucible. For example, doping impurities may be added. Mg is used as the P-type doping material, and Si is used as the N-type doping material. The shape of the crucible is not particularly limited and is, for example, a cylindrical shape (a circular cross section), but is not limited to a cylindrical shape. The shape of the crucible may be a cylinder with a non-circular cross section. When using a crucible with a non-circular cross section, the stirring efficiency of the melt by swinging the crucible is better than when using a crucible with a circular cross section.

Manufacture of a GaN single crystal using this apparatus can be performed, for example, as follows. First, a sapphire substrate on which a GaN crystal thin film layer is formed is placed in the crucible. On the other hand, in the glove box, gallium (Ga), metallic sodium (Na), carbon (C) Are weighed and placed in a crucible 15, and the crucible 15 is set in a pressure and heat resistant container 13. Then, nitrogen gas is supplied from the gas tank 11 into the heat and pressure resistant container 13. At this time, the pressure is adjusted to a predetermined pressure by the pressure regulator 12. Then, the inside of the heat and pressure resistant container 13 is heated by the electric furnace 14. Then, in the crucible 15, sodium dissolves to form a melt, and the nitrogen gas dissolves in the melt, and the nitrogen and gallium react in the presence of carbon, and the GaN on the substrate A GaN crystal grows on the thin film layer. In this crystal growth, since carbon is present in the melt, the generation of GaN crystal nuclei is prevented in the melt, and the GaN crystal grows on the GaN thin film layer on the substrate. The nonpolar plane (a-plane or M-plane) grows. For example, the crucible 15 corresponds to the “adjustment unit for adjusting the carbon content in the melt” of the present invention. For example, the crucible 15 corresponds to the “reaction portion where gallium and nitrogen react” of the present invention. The growth mechanism of the GaN crystal of the present invention is, for example, because carbon in the melt reacts with nitrogen and exists in the form of CN_ in the vicinity of the gas-liquid interface of the flux. It is estimated that the formation of miscellaneous crystals in can be avoided. Therefore, the production method of the present invention can also be used for the production of Group III element nitride crystals other than gallium as long as nitrogen and carbon are present. In the case of producing the group III element nitride crystal, the gallium may be replaced with another group III element (A1, in, etc.) or they may be used in combination. Examples of the group III element nitride crystal include Al Ga In (l—s—t) N (where 0≤s≤l, 0≤t≤l, s + t≤l).

s t

It is. In addition, this invention is not limited at all by the said estimation.

[0039] As described above, the production method of the present invention may further include a stirring step of stirring the melt. For example, if the reaction between gallium and nitrogen in the melt is performed in a state in which the melt and gallium are stirred and mixed, the dissolution rate of nitrogen in the mixture increases and the gallium in the melt Nitrogen is evenly distributed and fresh raw materials can be constantly supplied to the crystal growth surface, so that transparent, uniform dislocation density, low thickness, high quality and large, buttery transparent gallium nitride crystals can be produced quickly. Since it can manufacture, it is more preferable. In addition, for example, a GaN crystal having a smooth surface can be obtained.

[0040] In the present invention, the agitation step is not particularly limited. It may be performed with reference to the description, or may be performed by any other method. Specifically, the agitation step of the present invention can be carried out, for example, by swinging the heat and pressure resistant container, rotating the heat and pressure resistant container, or combining them. In addition, for example, the melt can be stirred by giving a temperature difference to the melt in the crucible. This is because thermal convection occurs in the melt. More specifically, for example, in addition to heating the heat and pressure resistant container for forming a melt, the heat and pressure resistant container is heated to generate thermal convection. Can be stirred and mixed. Furthermore, you may implement the said stirring process using a stirring blade. These stirring and mixing means can be combined with each other with a force S.

[0041] In the present invention, the swinging of the heat and pressure resistant container is not particularly limited. For example, after the heat and pressure resistant container is tilted in a certain direction, the direction is opposite to the direction described above. There is rocking that tilts the heat and pressure resistant container in a certain direction. Further, the rocking may be regular rocking or intermittent and irregular rocking. Moreover, the rotational motion may be used in combination with the swing. The inclination of the heat-resistant and pressure-resistant container during swing is not particularly limited. The period of oscillation in the regular case is, for example, 1 second to 10 hours, preferably 30 seconds to 1 hour, and more preferably 1 minute to 20 minutes. The maximum inclination of the heat-resistant pressure-resistant container in swinging is, for example, 5 to 70 degrees, preferably 10 to 50 degrees, more preferably 15 to 45 degrees with respect to the center line in the height direction of the heat-resistant pressure-resistant container. is there. Further, as will be described later, when the substrate is disposed at the bottom of the heat-resistant pressure-resistant vessel, the gallium nitride thin film on the substrate is always covered with the melt and may be swung. When the heat and pressure resistant container is tilted, the melt may be removed from the substrate.

[0042] Heating of the heat-resistant and pressure-resistant vessel for heat convection is not particularly limited as long as heat convection occurs. The heating position of the heat and pressure resistant container is not particularly limited, and for example, the bottom of the heat and pressure resistant container may be used, or the lower side wall of the heat and pressure resistant container may be heated. The heating temperature of the heat and pressure resistant container for the heat convection is, for example, 0.01 ° C to 500 ° C higher than the heating temperature for forming the melt, preferably 0.1 °. C to 300 ° C higher temperature, more preferably 1 ° C to higher; 100 ° C higher temperature. A normal heater can be used for the heating. [0043] The stirring step using the stirring blade is not particularly limited, and may be, for example, a rotational motion, a reciprocating motion, or a combination of the both motions of the stirring blade. Further, the stirring step using the stirring blade may be based on a rotational motion or a reciprocating motion of the heat and pressure resistant container with respect to the stirring blade, or a combination of the both motions. The stirring step using the stirring blade may be a combination of the motion of the stirring blade itself and the motion of the heat and pressure resistant container itself! /. The stirring blade is not particularly limited, and its shape and material are, for example, a force S that can be appropriately determined according to the size and shape of the heat and pressure resistant container, a nitrogen-free material having a melting point or decomposition temperature of 2000 ° C or higher. Formed by! /, Preferable to be! / ,. This is because a stirring blade formed of such a material can be prevented from being melted by the melt, and crystal nucleus formation on the surface of the stirring blade can be prevented.

[0044] Examples of the material of the stirring blade include rare earth oxides, alkaline earth metal oxides, W, SiC, diamond, diamond-like carbon, and the like. This is because, similarly to the above, the stirring blade formed of such a material can be prevented from being melted by the melt and can prevent crystal nucleation on the surface of the stirring blade. Examples of the rare earth and the alkaline earth metal include Sc, Y, La, Ce, Pr, Nd, Pm, Sm, Eu, Gd, Tb, Dy, Ho, Er, Tm, Yb, Be, Mg. , Ca, Sr, Ba, Ra force S. Preferred materials for the stirring blade are Y 2 O, CaO, MgO, W, SiC, diamond, and die.

twenty three

For example, yomon is the most preferred.

twenty three

Next, the full width at half maximum of the rocking curve of the two-crystal method X-ray diffraction of the GaN crystal of the present invention is preferably as low as possible within a range exceeding 0 and not exceeding 200 seconds. The full width at half maximum of the rocking curve of the two-crystal method X-ray diffraction is such that the X-ray incident from the X-ray source is highly monochromatic by the first crystal, irradiated to the GaN crystal as the second crystal, and diffracted from the GaN crystal It can be measured by calculating the FWHM (Full width at half maximum) centered on the peak of the X-ray. The X-ray source is not particularly limited, but for example, a CuKa line can be used. Also, the first crystal is not particularly limited! /, But, for example, an InP crystal or Ge crystal can be used.

[0046] The dislocation density of the GaN crystal of the present invention is in the range of more than 0 and 10 ⁶ pieces / cm ² or less, and the lower the better. The type of dislocation density is not particularly limited, for example, edge dislocation There is a screw dislocation. The method for measuring the dislocation density is not particularly limited. For example, it can be measured with a force S by observing and measuring the crystal structure of a group III element nitride crystal with a transmission electron microscope (TEM).

[0047] The GaN crystal of the present invention may contain carbon. The carbon may be derived from carbon in the melt, for example. The form of carbon contained in the group III element nitride crystal may be an atom, a molecule, or a compound with another element. The carbon content of the group III element nitride crystal is not particularly limited, if example embodiment, 10 ¹⁵ ~; 10 ²² / cm ^3, preferably in the range from 10 ¹⁶ to; 10 ²¹ / cm ³ The range is more preferably 10 ¹⁷ to; 10 ² ° / cm ³ . Since the GaN crystal obtained by the production method of the present invention contains carbon derived from carbon in the melt, if carbon is detected in a certain GaN crystal, it is the crystal produced by the production method of the present invention. It turns out that. In addition, since the method for producing the GaN crystal of the present invention is not particularly limited, carbon may not be included when produced by a method other than the production method of the present invention. The method for detecting carbon from the GaN crystal is not particularly limited, and can be detected by, for example, secondary ion mass spectrometry. The carbon ratio in the GaN crystal of the present invention is the same as described above. In addition, when the GaN crystal of the present invention contains carbon, it may be a P-type semiconductor.

Next, the substrate of the present invention includes the GaN crystal of the present invention. For example, the substrate of the present invention may be one in which a GaN crystal is formed on a GaN crystal thin film on a substrate such as sapphire by the production method of the present invention. In this case, it is preferable that the sapphire substrate or the like is peeled off to make a GaN crystal alone free-standing substrate. As shown in FIG. 1, when a semiconductor device such as an LED is formed on the substrate 1 of the present invention, a high-performance semiconductor device can be obtained, for example, a high-brightness LED. The type of the semiconductor device of the present invention is not particularly limited, and examples thereof include an LED, a semiconductor laser, and a power high frequency electronic element.

Example

Next, examples of the present invention will be described. However, the present invention is not limited to the following examples.

[0050] (Example 1)

A GaN crystal was manufactured using the apparatus shown in FIG. That is, first, the alumina crucible 1 5, a sapphire substrate on which a GaN thin film layer (the upper surface is c-plane) was formed. Further, sodium (Na), gallium (Ga) and carbon (C: graphite) were put into the alumina crucible 15 described above. The molar ratio of sodium (Na) to gallium (Ga) is Na: Ga = 73: 27. Also, the addition ratio of carbon (C), compared sodium (Na), the sum of gallium (Ga) and carbon (C) (Na + Ga + C), in atomic ^{_{0/0 (at.%)}} , 0 , 0.02, 0.1, 0.5, 1, 2, 5at.%. Oat.% Is Comparative Example 1. The crucible 15 was placed in a stainless steel container 13, and the stainless steel container 13 was placed in a heat and pressure resistant container 14. Nitrogen gas is introduced into the stainless steel container 13 from the gas tank 11 and simultaneously heated by a heater (not shown) to heat the heat and pressure resistant container 14 to 850 ° C., 40 atm (about 4. OMPa). The target GaN crystal was manufactured under the high-temperature and high-pressure conditions of 96 hours.

[0051] A photograph of the GaN crystal when the carbon addition is lat.% Is shown in FIG. 4, a photograph of the GaN crystal when the carbon addition ratio is 5 at.% Is shown in FIG. 5, and the carbon addition ratio is Oat Figure 6 shows a photograph of a GaN crystal in the case of% (Comparative Example 1). As shown in Fig. 6, the [0001] (c-plane) and [10-11] planes grow in the GaN crystal without carbon. On the other hand, as shown in Fig. 4, the [10 10] plane (M plane) grew in the GaN crystal when carbon was added at a rate of lat. As shown in Fig. 5, the [10-10] plane (M plane) grew greatly in the GaN crystal when carbon was added at a rate of 5 at.%. The graph in Fig. 7 shows the yield of GaN crystals at each carbon addition ratio. In the figure, the part represented by the white bar graph indicates the yield of GaN crystals grown on the GaN crystal thin film layer (LPE yield), and the part represented by the black bar graph represents nucleation in the melt. This is the yield of GaN crystals grown as a result (nucleation yield). As shown in the graph of Fig. 7, nuclei were generated when carbon was not added, but when carbon was added, nucleation was prevented and there was no decrease in LPE yield due to an increase in the amount of carbon added. It was.

[0052] (Example 2)

The reaction conditions for crystal growth were a temperature of 800 ° C, a pressure of 50 atm (about 5. OMPa), and the carbon addition ratio was Oat.% (Comparative Examples 2 and 3), lat.%, 2 at.%, 3 at A GaN crystal was produced in the same manner as in Example 1 except that it was changed to%. The result is shown in the graph of FIG. In the figure, the white bar graph represents the GaN crystal grown on the GaN crystal thin film layer. The portion represented by the black bar graph is the yield of the GaN crystal that is nucleated and grown in the melt (nucleation yield). In the figure, additive-free 1 is Comparative Example 2, and additive-free 2 is Comparative Example 3. As shown in the graph of FIG. 9, when no carbon was added, nuclei were generated and the growth of GaN crystals on the GaN crystal thin film layer was inhibited. However, when carbon was added, nucleation was prevented. On the GaN crystal thin film layer, a GaN crystal having a high-quality nonpolar surface was grown.

[0053] (Example 3)

The reaction conditions during crystal growth were a temperature of 750 ° C, a pressure of 50 atm (about 5. OMPa), and the carbon addition ratio was Oat.% (Comparative Examples 4, 5, 6), lat.%, 2 at.% A GaN crystal was produced in the same manner as in Example 1 except that the content was 3 at.%. The result is shown in the graph of FIG. In the figure, the white bar graph represents the yield of GaN crystals grown on the GaN crystal thin film layer (LPE yield), and the black bar graph represents nucleation in the melt. It is the yield (nucleation yield) of the grown GaN crystal. In the figure, additive-free 1 is Comparative Example 4, additive-free 2 is Comparative Example 5, and additive-free 3 is Comparative Example 6. As shown in the graph of FIG. 10, when no carbon was added, nuclei were generated and the growth of GaN crystals on the GaN crystal thin film layer was inhibited, but when carbon was added, nucleation was prevented, A GaN crystal having a high-quality nonpolar surface was grown on the GaN crystal thin film layer.

[Example 4]

In this example, a 2inch-GaN thin film (GaN thin film with a diameter of 5 cm, top surface is M-plane) grown on a sapphire substrate by MOCVD method was used as seed crystal, and carbon was added during the growth of Balta GaN single crystal. It was confirmed. The specific experimental procedure is as follows. That is, first, Gal 5 g and Nal 4.8 g were filled in an alumina crucible together with the seed substrate, and then a graphite as a carbon source was added so as to be 0.5 mol% with respect to Na. Then, epitaxial growth was performed for 96 hours at a growth temperature of 860 ° C and a growth pressure of 45 atm. As a result, a GaN single crystal (diameter about 5 cm) was epitaxially grown on the seed crystal substrate with a thickness of about 2 mm. This GaN single crystal is shown in the photograph in Fig. 12. The GaN crystal of this example is the world's largest crystal as a GaN single crystal currently reported. In this example, a GaN crystal (a) grown on a crucible and a GaN crystal grown epitaxially on the seed crystal The ratio of crystals (b) (a: b) was 2: 8. On the other hand, when the GaN single crystal was grown under the same conditions except that no carbon was added, the ratio (a: b) was 95: 5. Therefore, in the present invention, the addition of carbon suppresses the generation of nuclei on the crucible, promotes the epitaxial growth, and as a result, enables the growth of large crystals. It can be said that it was done.

Industrial applicability

As described above, according to the GaN crystal manufacturing method of the present invention, at least one of prevention of nucleation and growth of a high-quality nonpolar surface can be realized. If the GaN crystal of the present invention is used as, for example, a substrate, a high-performance semiconductor device can be manufactured. Therefore, the present invention is useful in the field of group III element nitride crystal semiconductors such as heterojunction high-speed electronic devices and optoelectronic devices (semiconductor lasers, light-emitting diodes, sensors, etc.).

Claims

The scope of the claims

[I] A method for producing a GaN crystal in a melt containing at least an alkali metal and gallium,

An adjusting step of adjusting the carbon content in the melt;

A reaction step in which the gallium and nitrogen react;

A method for producing a GaN crystal.

[2] The adjustment step according to claim 1, including at least one of a removal step of removing a part of carbon in the melt and an addition step of adding carbon to the melt. GaN crystal manufacturing method.

[3] including a seed crystal providing step of providing a seed crystal in the melt,

The GaN crystal manufacturing method according to claim 1, wherein the seed crystal is a GaN crystal.

[4] The GaN crystal manufacturing method according to claim 1, wherein the carbon is at least one of a carbon simple substance and a carbon compound.

[5] The Ga according to claim 3, wherein the seed crystal is a GaN crystal layer formed on a substrate.

N crystal manufacturing method.

[6] The method for producing a GaN crystal according to claim 3, wherein generation of crystal nuclei other than the seed crystal is prevented by adjusting a carbon content in the melt.

[7] The GaN crystal according to claim 6, wherein a content of carbon in the melt is in a range of 0.;! To 5 atomic% with respect to a total of the melt, the gallium, and the carbon. Production method.

[8] The method for producing a GaN crystal according to claim 1, wherein the nonpolar plane of the GaN crystal is grown by adjusting the content of carbon in the melt.

[9] The GaN crystal production according to claim 8, wherein a content of carbon in the melt is in a range of 0.3 to 8 atomic% with respect to a total of the melt, the gallium, and the carbon. Method.

[10] The method for producing a GaN crystal according to claim 1, wherein the melt is a melt containing Na.

[II] The method for producing a GaN crystal according to claim 10, wherein a nonpolar plane of at least one of the M plane and the a plane of the GaN crystal grows by adjusting a carbon content in the melt. .

[12] The upper surface of the GaN crystal layer on the substrate is a nonpolar surface. GaN crystal manufacturing method.

[13] The method for producing a GaN crystal according to claim 1, further comprising a stirring step of stirring the melt.

[14] Non-polar surface as the main surface, full width at half maximum of rocking curve by two-crystal method X-ray diffraction, exceeding SO and within 200 seconds or less, dislocation density exceeding 0 10 ⁶ / cm ² A GaN crystal in the following range.

[15] The GaN crystal according to claim 14, containing carbon.

[16] The GaN crystal according to claim 14, manufactured by the manufacturing method according to claim 1.

[17] A GaN crystal substrate comprising the GaN crystal according to claim 14, wherein the nonpolar surface is a substrate surface on which a semiconductor layer is formed.

[18] A semiconductor device comprising the substrate according to claim 17, wherein a semiconductor layer is formed on the substrate surface.

[19] The semiconductor device according to claim 18, wherein the semiconductor device is an LED, a semiconductor laser, or a power high-frequency electronic element.

[20] A production apparatus for producing a GaN crystal in a melt containing at least an alkali metal and gallium,

A preparation unit for adjusting the content of carbon in the melt;

An apparatus for producing a GaN crystal, comprising: a reaction section in which the gallium and nitrogen react.